The color of glass
When it comes to beauty and color, I cannot think of any material that can match the beautiful hues of glass. Even colorless glass produces a fascinating rainbow palette as soon as sun rays break through.
Variation by metal
There is a wide variety of colors available to us, both in opaque and transparent glass.
The difference between the two is very simple: transparent glass lets light through, opaque (almost) does not. Both are equally suitable for flamework.
Although glass exists in just about every color you can think of, there is a big difference in price and quality between, say, blue, red or white glass. This is because metals (or metal oxides) are added during the production process to color the glass. And even if it's only micro particles, a color that requires gold will always be more expensive than a color that can be obtained with copper.
And then you have the “speciallekes” like striking glass and black-that-isn't-black. Intense black is apparently an incredibly difficult color to make.
What is sold as black glass is in fact often dark purple. and there is also glass that at first glance appears dull monochrome and after processing turns into a mix of colors or takes on a beautiful silver sheen.
Strike
If a type of glass is labeled “striking,” it means that its true color will not emerge until later, when the glass is heated in the burner or in the oven at a certain temperature.
So don't be alarmed if you order some rods bright red glass online and get a colorless bundle delivered to you. This is not an incorrect delivery, but the beautiful bright red will only show up when processed.
To activate a striking color you make the glassware as usual in a neutral flame. You let it harden until it stops glowing, but don't let it get too cold so it doesn't crack. Then you hold the glass again in the top of the flame (the coldest part) until the color appears. Of course, while doing this you must be careful not to melt and deform the glass again.
Some “striking” colors require an oxidizing flame (a flame with more oxygen), but there are also types of glass where the color or a beautiful metallic sheen only appears in a flame with less oxygen supply.
